In theory, this would be an excellent concept for a game, but probably not for a super-epic, you're the chosen one AGAIN, and the world is doooooooomed sort of game. In practice, especially with that sort of plot, I imagine that most people would just get upset with the time restriction, because if not done right that's all it would turn into. If things developed more procedurally, though, rather than along a set path, then I can see players being more forgiving.

A friend and I played around with this concept a few years ago. We didn't get very far, of course, since we both had degrees to focus on instead of complicated procedural gameplay, but I still find myself going back to the idea quite a lot.

Imagine if, for instance, a graveyard outside of town attracted a necromancer. His army of the dead would keep growing until he and the town came to blows. Maybe the village gets wiped out, leading to a small kingdom of the mindless dead, unless of course a hero wanders along at some point and stops him. Or maybe it's a dragon. Or maybe it's a giant, agressive kingdom to the north, all reacting to each other and creating a virtual ecosystem of sorts that manages to operate completely without player intervention.

It's all very possible, if complicated. Just look at Dwarf Fortress. I'd love to see a bigger company give something like this a try, but as I said, it would have to be done very carefully to keep it from turning into just another type of time limit.